Nature, 17 August 2023, VOL 620, ISSUE 7974
《自然》2023年8月17日，第620卷，7974期
物理学Physics
Microstructure and crystal order during freezing of supercooled water drops
过冷水滴冻结过程中的微观结构和结晶有序
▲ 作者：Armin Kalita, Maximillian Mrozek-McCourt, Thomas F. Kaldawi, Philip R. Willmott, N. Duane Loh, Sebastian Marte, et al.
▲ 链接：
https://www.nature.com/articles/s41586-023-06283-2
▲ 摘要：
过冷水滴被广泛用于研究过冷水、冰成核和液滴冻结。过冷水滴在大气中的冻结影响云的动力学和气候反馈，并通过二次冰的产生加速云的冻结。液滴冻结发生在几个时间尺度和长度尺度上，并且具有足够的随机性，使两个冻结的液滴不可能完全相同。
研究组使用光学显微镜和X射线激光衍射研究了真空中数万个水微滴在约234~235K均质冰成核后的冻结过程。在水滴图像的基础上建立了一个七阶段冻结模型，并用该模型对衍射数据计时。
冰晶衍射结果表明，长程晶序在冻结后不到1ms的时间内形成，而剩余液体的衍射结果则与预融冰上的准液体层相似。冰刚冻结时具有应变的六方晶体结构，这是一种早期亚稳态，可能先于具有堆叠缺陷的冰形成。
该技术可助力确定其他条件下的冻结动力学，比如云中的水滴冻结，或助力理解其他材料的快速凝固。
▲ Abstract：
Supercooled water droplets are widely used to study supercooled water, ice nucleation and droplet freezing. Their freezing in the atmosphere affects the dynamics and climate feedback of clouds and can accelerate cloud freezing through secondary ice production. Droplet freezing occurs at several timescales and length scales and is sufficiently stochastic to make it unlikely that two frozen drops are identical. Here we use optical microscopy and X-ray laser diffraction to investigate the freezing of tens of thousands of water microdrops in vacuum after homogeneous ice nucleation around 234–235 K. On the basis of drop images, we developed a seven-stage model of freezing and used it to time the diffraction data. Diffraction from ice crystals showed that long-range crystalline order formed in less than 1 ms after freezing, whereas diffraction from the remaining liquid became similar to that from quasi-liquid layers on premelted ice. The ice had a strained hexagonal crystal structure just after freezing, which is an early metastable state that probably precedes the formation of ice with stacking defects. The techniques reported here could help determine the dynamics of freezing in other conditions, such as drop freezing in clouds, or help understand rapid solidification in other materials.
材料科学Materials Science
Reversible spin-optical interface in luminescent organic radicals
发光有机自由基的可逆自旋光界面
▲ 作者：Sebastian Gorgon, Kuo Lv, Jeannine Grüne, Bluebell H. Drummond, William K. Myers, Giacomo Londi, et al.
▲ 链接：
https://www.nature.com/articles/s41586-023-06222-1
▲ 摘要：
分子为量子信息科学提供了一个通用平台，是传感和计算应用的候选者。稳健的自旋光学界面是利用材料量子资源的关键。迄今为止，碳基候选材料均不发光，这限制了通过发射进行光学读出。
研究组报道了自旋多重性S>1时，具有高效发光且激发态近单位产率的有机分子。基于设计发射双重态和三重态能级之间的能量共振，实现了三（2,4,6-三氯苯基）甲基咔唑自由基和蒽的共价偶联。
研究组观察到，双光子激发在几皮秒内离域到连接并苯上，并随后演化为1.8 eV附近混合自由基-三重态特征的纯高自旋态（单自由基为四重态，双自由基为五重态）。即使在295K下，这些高自旋态也可用于微波相干寻址，通过反向系间窜越到发射态来实现光学读出。
此外，对于双自由基，在返回基态时，先前不相关的自由基自旋在蒽的两侧均显示出很强的自旋相关性。该方法在室温下同时支持高效初始化、自旋调控和基于光的读出。发光和高自旋态集成为新兴量子技术创造了一个有机材料平台。
▲ Abstract：
Molecules present a versatile platform for quantum information science and are candidates for sensing and computation applications. Robust spin-optical interfaces are key to harnessing the quantum resources of materials. To date, carbon-based candidates have been non-luminescent, which prevents optical readout via emission. Here we report organic molecules showing both efficient luminescence and near-unity generation yield of excited states with spin multiplicity S > 1. This was achieved by designing an energy resonance between emissive doublet and triplet levels, here on covalently coupled tris(2,4,6-trichlorophenyl) methyl-carbazole radicals and anthracene. We observed that the doublet photoexcitation delocalized onto the linked acene within a few picoseconds and subsequently evolved to a pure high-spin state (quartet for monoradical, quintet for biradical) of mixed radical–triplet character near 1.8 eV. These high-spin states are coherently addressable with microwaves even at 295 K, with optical readout enabled by reverse intersystem crossing to emissive states. Furthermore, for the biradical, on return to the ground state the previously uncorrelated radical spins either side of the anthracene shows strong spin correlation. Our approach simultaneously supports a high efficiency of initialization, spin manipulations and light-based readout at room temperature. The integration of luminescence and high-spin states creates an organic materials platform for emerging quantum technologies.
Autonomous healing of fatigue cracks via cold welding
疲劳裂纹的冷焊自动修复
▲ 作者：Christopher M. Barr, Ta Duong, Daniel C. Bufford, Zachary Milne, Abhilash Molkeri, Nathan M. Heckman, et al.
▲ 链接：
https://www.nature.com/articles/s41586-023-06223-0
▲ 摘要：
金属疲劳是指在重复机械载荷作用下，通过裂纹的增量扩展而逐渐失效。在结构应用中，疲劳占在役失效的90%。疲劳的预防依赖于大安全系数和低效过度设计的实施。在传统的抗疲劳冶金设计中，人们开发微观结构来阻止或减缓裂纹的发展。
裂纹生长被假定为不可逆的。相比之下，在其他材料类别中，存在一种基于潜在修复机制和伤害逆转的令人信服的替代方案。
研究组报道了纯金属的疲劳裂纹也可以进行内在自修复。他们直接观察到纳米级疲劳裂纹的早期发展，不出所料，裂纹在局部微观结构障碍处前进、偏转和停止。然而，出乎意料的是，裂纹也被观察到通过局部应力状态和晶界迁移共同引发的裂纹侧面冷焊过程而自我修复。
疲劳裂纹可通过与微观结构特征的局部相互作用而在金属中自动修复，这一假设对工程师如何设计和评估结构材料疲劳寿命的最基本理论提出了挑战。研究组讨论了在各种服务环境中疲劳会有何影响。
▲ Abstract：
Fatigue in metals involves gradual failure through incremental propagation of cracks under repetitive mechanical load. In structural applications, fatigue accounts for up to 90% of in-service failure. Prevention of fatigue relies on implementation of large safety factors and inefficient overdesign. In traditional metallurgical design for fatigue resistance, microstructures are developed to either arrest or slow the progression of cracks. Crack growth is assumed to be irreversible. By contrast, in other material classes, there is a compelling alternative based on latent healing mechanisms and damage reversal. Here, we report that fatigue cracks in pure metals can undergo intrinsic self-healing. We directly observe the early progression of nanoscale fatigue cracks, and as expected, the cracks advance, deflect and arrest at local microstructural barriers. However, unexpectedly, cracks were also observed to heal by a process that can be described as crack flank cold welding induced by a combination of local stress state and grain boundary migration. The premise that fatigue cracks can autonomously heal in metals through local interaction with microstructural features challenges the most fundamental theories on how engineers design and evaluate fatigue life in structural materials. We discuss the implications for fatigue in a variety of service environments.
能源科学Energy Science
Inverted perovskite solar cells using dimethylacridine-based dopants
使用二甲基吖啶掺杂剂的倒置钙钛矿太阳能电池
▲ 作者：Qin Tan, Zhaoning Li, Guangfu Luo, Xusheng Zhang, Bo Che, Guocong Chen, et al.
▲ 链接：
https://www.nature.com/articles/s41586-023-06207-0
▲ 摘要：
钙钛矿半导体掺杂及其晶界钝化仍颇具挑战性，但对于推进高效钙钛矿太阳能电池至关重要。尤其是在不预先沉积一层空穴传输材料的情况下，构建基于钙钛矿/氧化铟锡（ITO）肖特基接触的倒置器件至关重要。
研究组报道了一种基于二甲基吖啶的分子掺杂工艺，用于构建匹配良好的p-钙钛矿/ITO接触以及晶界的全面钝化，并实现了25.39%的认证功率转换效率（PCE）。在氯苯淬火结晶过程中，分子从前驱体溶液挤压到晶界和薄膜表面底部，被称之为分子挤压过程。
分子的去质子化磷酸基团与钙钛矿聚碘化铅之间的核配位配合物既负责机械吸收又负责电子电荷转移，导致了钙钛矿膜的p型掺杂。研究组创造了一种PCE为25.86%（反向扫描）的高效设备，在光照1000小时后仍保持96.6%的初始PCE。
▲ Abstract：
Doping of perovskite semiconductors and passivation of their grain boundaries remain challenging but essential for advancing high-efficiency perovskite solar cells. Particularly, it is crucial to build perovskite/indium tin oxide (ITO) Schottky contact based inverted devices without predepositing a layer of hole-transport material. Here we report a dimethylacridine-based molecular doping process used to construct a well-matched p-perovskite/ITO contact, along with all-round passivation of grain boundaries, achieving a certified power conversion efficiency (PCE) of 25.39%. The molecules are shown to be extruded from the precursor solution to the grain boundaries and the bottom of the film surface in the chlorobenzene-quenched crystallization process, which we call a molecule-extrusion process. The core coordination complex between the deprotonated phosphonic acid group of the molecule and lead polyiodide of perovskite is responsible for both mechanical absorption and electronic charge transfer, and leads to p-type doping of the perovskite film. We created an efficient device with a PCE of 25.86% (reverse scan) and that maintained 96.6% of initial PCE after 1,000 h of light soaking.
地球科学Earth Science
Future emergence of new ecosystems caused by glacial retreat
冰川退缩导致未来新生态系统的出现
▲ 作者：J. B. Bosson, M. Huss, S. Cauvy-Fraunié, J. C. Clément, G. Costes, M. Fischer, et al.
▲ 链接：
https://www.nature.com/articles/s41586-023-06302-2
▲ 摘要：
与人为气候变化相关的冰川萎缩和冰后期生态系统的发展是某种持续时间最快的生态系统变化，具有显著的生态和社会连锁后果。然而，据人们所知，目前还没有完整的空间分析来量化或预测这种重要转变。
研究组表明，到2100年，南极和格陵兰冰盖以外所有冰川的减少可能会产生新的陆地、海洋和淡水生态系统，面积范围从尼泊尔（149,000±55,000平方千米）到芬兰（33.9,000±99,000平方千米）不等。该分析表明，冰川面积的损失将在22±8%至51±15%之间，具体取决于气候情景。
在冰川消融地区，新兴生态系统将以极端到温和的生态条件为特征，为适应寒冷的物种提供庇护，或有利于初级生产力和广幅种。面对气候变化、生物多样性丧失和淡水稀缺，探索冰川地区的未来凸显了冰川和新兴冰后期生态系统的重要性。
而目前只有不到一半的冰川区位于保护区。研究组赞同联合国最近宣布2025年为国际冰川保护年的决议和《全球生物多样性框架》，强调迫切需要同时加强减缓气候变化和对这些生态系统的就地保护，以确保其存在、功能和价值。
▲ Abstract：
Glacier shrinkage and the development of post-glacial ecosystems related to anthropogenic climate change are some of the fastest ongoing ecosystem shifts, with marked ecological and societal cascading consequences. Yet, no complete spatial analysis exists, to our knowledge, to quantify or anticipate this important changeover. Here we show that by 2100, the decline of all glaciers outside the Antarctic and Greenland ice sheets may produce new terrestrial, marine and freshwater ecosystems over an area ranging from the size of Nepal (149,000 ± 55,000 km2) to that of Finland (339,000 ± 99,000 km2). Our analysis shows that the loss of glacier area will range from 22 ± 8% to 51 ± 15%, depending on the climate scenario. In deglaciated areas, the emerging ecosystems will be characterized by extreme to mild ecological conditions, offering refuge for cold-adapted species or favouring primary productivity and generalist species. Exploring the future of glacierized areas highlights the importance of glaciers and emerging post-glacial ecosystems in the face of climate change, biodiversity loss and freshwater scarcity. We find that less than half of glacial areas are located in protected areas. Echoing the recent United Nations resolution declaring 2025 as the International Year of Glaciers’ Preservation and the Global Biodiversity Framework, we emphasize the need to urgently and simultaneously enhance climate-change mitigation and the in situ protection of these ecosystems to secure their existence, functioning and values.
Enhanced inner core fine-scale heterogeneity towards Earth’s centre
向地球中心增强的内核精细尺度非均质性
▲ 作者：Guanning Pang, Keith D. Koper, Sin-Mei Wu, Wei Wang, Marine Lasbleis & Garrett Euler
▲ 链接：
https://www.nature.com/articles/s41586-023-06213-2
▲ 摘要：
地球内核在流体外核内凝固时获得了“纹理”。组成纹理的大部分铁粒的大小、形状和方向记录了内核的生长，并可能随地质时间的推移而演变，以响应地球动力和扭矩。地震产生的地震波可用来成像地核的纹理或织构，从而深入了解地核的历史和演变。
研究组观察和模拟了在更大规模上构成内核织构的精细尺度（小于10km）非均质性反向散射的地震能量。使用一个由全球小孔径地震阵列（用于探测地下核爆炸的微小信号）创建的新数据集，以建立内核精细尺度非均质性的三维模型。
该模型显示，内核散射普遍存在，存在于所有采样的经纬度上，并且在内核边界以下500~800km处强度显著增加。在较深内核中增强的散射与延迟成核后的快速增长时代相兼容。
▲ Abstract：
Earth’s inner core acquires texture as it solidifies within the fluid outer core. The size, shape and orientation of the mostly iron grains making up the texture record the growth of the inner core and may evolve over geologic time in response to geodynamical forces and torques. Seismic waves from earthquakes can be used to image the texture, or fabric, of the inner core and gain insight into the history and evolution of Earth’s core. Here, we observe and model seismic energy backscattered from the fine-scale (less than 10 km) heterogeneities that constitute inner core fabric at larger scales. We use a novel dataset created from a global array of small-aperture seismic arrays—designed to detect tiny signals from underground nuclear explosions—to create a three-dimensional model of inner core fine-scale heterogeneity. Our model shows that inner core scattering is ubiquitous, existing across all sampled longitudes and latitudes, and that it substantially increases in strength 500–800 km beneath the inner core boundary. The enhanced scattering in the deeper inner core is compatible with an era of rapid growth following delayed nucleation.
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